1. Field of the Invention
The present invention relates to an ink jet printer, and specially to an ink jet printer comprising a main tank and a sub tank as an ink tank to store ink.
2. Description of the Related Art
Various printers have been developed such as an ink jet printer, a laser printer, a thermal transfer printer, a dot impact printer, a dye sublimation printer and the like as a recording terminal connected to a word processor, a personal computer and the like. Among them, the ink jet printer has advantages such as that it is quiet compared to other types of printers and it can easily record colorful images at low cost and the like, so that the ink jet printer is popular among the printers.
The ink jet printer comprises a recording head having a plurality of nozzles for jetting ink supplied from an ink tank as a droplet, and forms an image on a recording medium based on image information by jetting the ink from each nozzle of the recording head.
Conventionally, as a detection method to detect remaining ink amount in the ink tank, one in which electrodes for detection are used and the remaining ink amount is detected from a value of resistance between the electrodes (refer to JP-Tokukaisyo-59-194856 and JP-Tokukaihei-8-80619), one in which the remaining ink amount is detected from the shape change of an ink bag (refer to JP-Tokukaisyo-57-34966), one in which the remaining ink amount is judged by detecting power variation by a section to detect temperature (refer to JP-Tokukaihei-5-220974) or the like has been known.
However, in the case of using the electrodes as described in JP-Tokukaisyo-59-194856 and JP-Tokukaihei-8-80619, the ink in the ink bag may be electrolyzed by the electrodes.
To detect the shape change of the ink bag as described in JP-Tokukaisyo-57-34966, many components have to be attached to the ink bag itself, thereby raising cost.
Further, judging the remaining ink amount by detecting temperature change as described in JP-Tokukaihei-5-220974 raises a problem of time-consuming.
Further, in the above conventional ink jet printers, the ink tank needs to be arranged lower than the recording head to create negative pressure. In the case of printing large quantities such as in the recent ink jet printer, a large capacity ink tank needs to be arranged near a platen. Thus, in the case of comprising a plurality of the ink tanks, wide width is occupied, thereby making the body of the ink jet printer extremely large.
Thus, a sub tank to create negative pressure is provided, and the ink bag (main tank) is arranged at any position, so that the area occupied by the body of the printer can be small. However, in such structure, regarding to the replacement time of the main tank, conventionally, when the ink supplied to the main tank from the sub tank runs out, the sub tank becomes the state where there is a little ink therein to cause troubles such as jet failure or the like, and then a user judges that there is no remaining ink amount in the main tank for the first time. Thus, the user knows only vague ink amount in the main tank, so that there is a problem that the replacement time cannot be specified.